This invention relates to novel starch ether derivatives and to a method for the preparation thereof. This invention also relates to the use of the novel anionic or amphoteric starch ether derivatives as pigment retention aids in papermaking processes.
As used herein, the term "amphoteric starch ether derivative" refers to a starch ether derivative containing both cationic and anionic substituent groups.
The term "paper" as used herein includes sheet-like masses and molded products made from fibrous cellulosic materials which may be derived from natural sources as well as from synthetics such as polyamides, polyesters, and polyacrylic resins, and from mineral fibers such as asbestos and glass. In addition, papers made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is also included within the broad term "paper".
It is well known in the art to add anionic substituent groups to starch to form anionic and amphoteric starch ester and ether derivatives. Typical of the anionic substituent groups found in starch derivatives of the prior art are carboxyalkyl groups, sulfoalkyl groups, phosphate groups, and the like. A discussion of various starch ether derivatives containing these and other anionic groups can be found in "Starch: Chemistry and Technology", Vol. II, ed. by R. L. Whistler and E. F. Paschall (New York: Academic Press, 1967), pages 312-326. Among the reagents used to prepare carboxyalkyl starch ether derivatives are included sodium chloroacetate and salts of 1-halocarboxylic acids such as sodium 1-chloropropionate (see U.S. Pat. No. 2,523,709), sodium 1-bromopropionate, and sodium 1-bromoisovalerate (see German Pat. No. 717,275). Typical reagents used to prepared sulfoalkyl starch ether derivatives are sodium haloalkyl sulfonates such as, for example, sodium 2-haloethyl sulfonates (see U.S. Pat. Nos. 2,883,375 and 2,802,000), and sodium 3-chloro-2-hydroxypropyl sulfonate (see U.S. Pat. Nos. 2,825,727 and 2,806,857).
Sulfocarboxyalkyl starch ester derivatives are also known from the prior art, e.g., U.S. Pat. No. 4,029,544 to Jarowenko et al. teaches a pigment retention aid comprising an amphoteric starch ester derivative containing sulfosuccinate groups and cationogenic or cationic nitrogen-containing groups. Starch derivatives containing sulfocarboxyalkyl ether substituents, however, have not yet been disclosed.
Pigment retention aids per se are also well known in the art. In the case of paper containing added pigments, these materials are added to the pulp or stock during the papermaking process for the specific purpose of retaining a greater proportion of such pigments in the paper (rather than have them drain off in the water that is removed during the formation of the sheet). A particularly desirable pigment retention aid in paper is one which is effective at the higher alum concentrations often found in the paper industry, particularly in connection with the increasing utilization of recycled water.
It has been proposed to use starch phosphates as pigment retention aids, and their effectiveness has been noticeable with paper stock containing low to moderate concentrations of alum. At higher alum concentrations, however, the effectiveness of starch phosphates declines, due to reasons not readily understood. Possibly this is because the phosphate groups function as weak acids which are incapable of providing desired pigment retention in the presence of alum concentrations of greater than 4 percent, by weight, or the dry pulp. Thus, starch phosphates, or di- and trialkyl aminoalkyl starch phosphates, like other anionic or amphoteric starch derivatives of the prior art which are effective at lower concentrations of alum, are inferior at higher alum concentrations.
The amphoteric sulfocarboxyalkyl starch ester derivatives of Jarowenko et al. mentioned hereinabove have been found to improve the pigment retention of paper containing alum concentrations above 4 percent by weight, of the dry pulp. The preparation of the starch derivatives of Jarowenko et al., however, typically involves a somewhat laborious and uneconomical procedure whereby the starch base, which ordinarily must first be acid-converted to a water fluidity of at least 4 and not more than 40, is reacted with a reagent which provides the cationic substituent groups, then esterified with maleic anhydride, and finally sulfonated with sodium metabisulfite. Hence, the search continues for other starch derivatives which will improve pigment retention in paper at high concentrations of alum while being at the same time relatively facile and inexpensive to prepare.
Accordingly, it is an object of the present invention to provide novel anionic and amphoteric starch ether derivatives.
It is another object to provide anionic sulfocarboxyalkyl ether substituents for starch which substituents are relatively stable in alkaline medium.
It is a further object to provide a method for preparing starch ether derivatives which is both economical and convenient.
It is a still further object to provide anionic and amphoteric starch ether derivatives which act efficiently as pigment retention aids in paper having high alum acidity.